Up until version 6 came out, there was an ability to set an global input for audio where no-matter what shot composition or arrangement you had, you were only ever using the interface plus whatever each of the shots added. For most events, I'm finding that I lose a complete layer simply because I dedicate the bottom most one to a single audio interface input now. With the audio re-build that happened a few versions ago, and the audio mixer available, it would seemingly be easy to add a universal input like an external mixer.